The present invention relates to an arrangement for recognizing an imminent rollover of a vehicle which determines a critical yaw rate of the vehicle about its longitudinal axis, which would be required to cause the vehicle to roll over, as a function of the angle of inclination of the vehicle about its longitudinal axis.
According to German Published Patent Application No. 197 44 083, the critical yaw rate corresponds to a rotation energy of the vehicle, which just exceeds the potential energy of the vehicle. Namely, if this is the case, i.e., the critical yaw rate is attained, the vehicle will certainly roll over. This allows early prediction of a vehicle rollover, so that the safety devices fitted in the vehicle (e.g., airbags, roll bars, etc.) can be deployed in a timely manner prior to the actual rollover. With the aforementioned criterion which determines a critical yaw rate, an imminent rollover can be recognized with a high degree of reliability during driving maneuvers, in which the center of gravity of the vehicle is raised by a certain height in the earth""s gravity field, for example, when driving through a ramp, while the vehicle is in contact with the ground. When driving through a ramp in this manner, the energy of the vehicle is converted from rotation energy into potential energy. Driving on an embankment, when the car travels over an embankment and tips over as a result, represents another driving maneuver. Contrary to traveling through a ramp, in the case of driving over an embankment potential energy is converted into rotation energy; namely, the vehicle tips down the embankment without any external influencing factor (except for the force of gravity). It can be seen that the aforementioned criterion, known from German Published Patent Application No. 197 44 083, according to which a critical yaw rate is determined in order to recognize an imminent rollover, is not suitable for tipping over on an embankment, since it makes a premature rollover decision. Another criterion, described in German Published Patent Application No. 197 44 083, which can be referred to as angular criterion, is also not suitable for timely recognition of a rollover. This angular criterion is based on the fact that yaw rate signals delivered by a yaw rate sensor are filtered and integrated over a certain period of time. The resulting mean angle corresponds, with good approximation, to the actual current angle of inclination of the vehicle which is compared to a vehicle-specific critical angle starting at which the situation of the vehicle becomes unstable. The angular criterion has the disadvantage that it makes the decision of whether or not the vehicle will roll over relatively late, namely only when the vehicle-specific critical angle of inclination has been attained.
An object of the present invention is therefore to provide an arrangement of the aforementioned type which recognizes an imminent rollover in the event of a driving maneuver such as tipping over an embankment in a timely manner, i.e., neither too early nor too late.
The aforementioned object is achieved by the fact that in the event the arrangement detects a motion behavior of the vehicle that is characteristic for tipping over an embankment, it determines a predictive value of the yaw rate of the vehicle after a fictitious impact of the wheels on one longitudinal side of the vehicle against the ground from a yaw rate prevailing prior to the fictitious impact, the momentum of the vehicle in the direction of its vertical axis, and the angular momentum about the center of gravity of the vehicle prior to the fictitious impact, and it signals an imminent rollover if the predictive value of the yaw rate exceeds a critical yaw rate.
In the special case of traveling down over an embankment, where the potential energy of the vehicle is converted into rotation energy, the application of a balance of momentums according to the present invention for determining a predictive value of the yaw rate of the vehicle after tipping over the edge of an embankment results in timely recognition of a situation leading to a rollover.